But this is the first time we have a concrete number on how many Conservatives are actually lining up against the Prime Minister. The Conservatives for Britain group, formed on Sunday, is calling for the UK to have a veto on EU laws and wants an end to freedom of movement.

If Cameron fails to secure these tough new measures — a serious risk— it could spell disaster for Cameron. The Conservatives have a majority of just 12 in the House of Commons and if any of the MPs that have promised to fight against Europe decide to defect or stage a backbench rebellion, the current government could collapse. This would force a coalition or hung parliament.